13D Filing: Magnolia Infrastructure Holdings, LLC and American Midstream Partners LP (AMID)

---

ITEM 3.

Source and Amount of Funds or Other Consideration.

Item 3 is hereby supplemented with respect to the
disposition of securities reported hereby as follows:

On October 2, 2017, pursuant to the terms of the Fifth Amended and Restated Agreement of Limited
Partnership, as amended (the Partnership Agreement), of American Midstream Partners, LP (AMID), AMID exercised its call right to repurchase all of the 2,333,333 outstanding Series D Convertible Preferred Units representing
limited partner interests in AMID (Series D Units) from Magnolia Infrastructure Holdings, LLC for approximately $37.0 million in cash. After the closing date of such redemption, which occurred on October 2, 2017, no Series D Units remain
outstanding.

The foregoing is a summary only and the terms and conditions of the Partnership Agreement are qualified in their entirety by reference to
the Partnership Agreement, which are incorporated by reference into this Schedule 13D as set forth in Item 7 wherever such references and descriptions appear.

ITEM 4.

Purpose of Transaction.

The information set forth or incorporated in Item 3 is incorporated herein by
reference.

ITEM 5.

Interest in Securities of the Issuer.

Item 5 is hereby amended as follows:

(a)-(c) The information contained on the cover pages to this Amendment No. 20 to Schedule 13D and the information set forth and incorporated by reference
in Item 3 are incorporated herein by reference.

ITEM 7.

Material to be Filed as Exhibits.

See the Exhibit Index following the signature pages hereto.

13